For convenience, the invention will be described with particular reference to catalytic converters and particulate traps for diesel engines.
Internal combustion engines, whether spark or compression ignited, and due to incomplete combustion of the hydrocarbon fuel, often emit particulate material in the exhaust gases which is, for the most part finely divided carbon which may contain absorbed unburned hydrocarbons, sulfuric acid, nitrogen oxides, and other undesirable combustion by-products. Over the past several years, effort has been made to abate or materially reduce the highly visible "black" exhaust of diesel powered trucks, semis, off-the-road vehicles, and passenger cars. Although numerous devices utilizing honeycomb catalyst support members both ceramic and metallic have been suggested, (See for example "Diesel Particulate Control" P-158, SAE, The Engineering Resource for Advancing Mobility, International Congress and Exposition, Detroit, Mich., Feb. 25 1985-Mar. 1 1985 (ISBN 0-89883-719-7)) none is particularly effective where the exhaust is laden with particulate carbon. For examples of such devices, reference may be had to the patents to Retallick U.S. Pat. Nos. 4,402,871 dated Sept. 6 1983, 4,301,039 dated Nov. 17 1981, the patent to Chapmen et al. 4,318,888 dated Mar. 9 1982, and German Offenlegungsschrift No. 2,815,317, dated Oct. 18 1979. Suitable catalysts, e.g., platinum, palladium, and/or rhodium are on the surface of the honeycomb whether ceramic or metallic where it is firmly held and where the exhaust gases come into contact with the catalyst on the support surface. Under the combined effects of catalyst, oxygen, temperature, etc., the noxious oxides are converted to harmless gases and unburned hydrocarbons ignited and destroyed. This technology is at hand. See, for example the patent to Chapman U.S. Pat. No. 4,318,888, supra. Reference may also be had to U.S. Pat. Nos. 3,966,646 dated June 29 1976, 3,867,313 dated Feb. 18 1975, 3,873,472 dated Mar. 25 1975 to Oshima et al; U.S. Pat. No. 4,188,309 dated Feb. 12 1980 to Volker et al, all of which are directed to various catalyst systems and elements.
The foregoing typically have continuous tubular cells. In some cases, the cells may be blocked at one end for the purpose of forcing the gas containing the finely divided particulates to pass through the side wall of the ceramic cell to enter an adjacent cell which is open to permit exit of the filtered gas to the atmosphere. These devices of the "honeycomb" type devices are not particularly suitable for use with diesel engines. As indicated above, considerable effort has been expended in making all metal devices for control of exhaust emissions from diesel engines. However, the flow of exhaust gas through the metallic catalyst support media of the prior art has usually been along one catalyst coated side or between spaced catalyst coated sides from entrance to exit, also along continuous tubular pathways into and out of the catalytic unit. The gas flow has been parallel to the corrugations or the elongated tubular catalyst cells. Carbon suspended in the exhaust is virtually unaffected by the catalyst, although some carbon may burn along with unburned hydrocarbon in the exhaust in the presence of air which may be introduced for the purpose. The gas velocity and exhaust temperature is such that most of the particulate carbon escapes any conversion and is vented to the air as an offensive black smoke especially when the engine is under heavy load, e.g., at start up from rest.
The patents to Retallick U.S. Pat. Nos. 4,301,039 dated Nov. 17 1981 and 4,402,871 dated Sept. 6 1983 disclose forms of metallic catalyst support unit characterized by a series of discontinuous displacements of metal out of the plane of a metal strip in each direction relative to the surface, i.e., elevated and depressed. These displacements are elongated and have an axial dimension longer than the depth of the displacement out of the plane of the metal strip. The elongated displacements lie with their axes normal to the marginal edges of the strip. There is a plurality of such displacements across the width of the strip. Such discontinuous displacements may have their axes along a line perpendicular to the marginal edges, or adjacent displacements may be longitudinally spaced relative to the longitudinal axis of the metal strip. This arrangement is disclosed in U.S. patent application No. 648,381 filed Sept. 7 1984 by W. B. Retallick. Whatever the geometry of these bumps and depressions, the objective has been to flow a particulate-containing gas between confronting and contacting surfaces of a flat plate and a plate having bumps and/or depressions in a direction normal to the longitudinal extent of the bump or depression. The purpose of this configuration and gas flow pattern is to cause the gas to flow along a tortuous path and undergo abrupt changes in direction resulting in the entrained particles being thrown out of the gas stream whereby the particles collect in "clefts" formed by the "bumps" and a contiguous plate or member. Such action causes a build-up of carbon particles which if too long continued will plug the catalytic converter. Consequently, means are provided which for convenience may be responsive to back pressure in the system for shifting the exhaust to a parallel regenerated catalytic converter free of accumulated carbon or into a by-pass line. A system including a pressure responsive plate valve may be used for this purpose.
There are several known ways of regenerating the trap or catalytic converter trap. These generally involve combusting the carbon and any absorbed hydrocarbon or other pollutant to form carbon dioxide and water plus minor amounts of other oxides. To accomplish this, additional air and fuel may be introduced into the trap or converter, and if the temperature is sufficient, the carbon will ignite spontaneously. The presence of oxidation catalysts in the converter/trap will also aid in regeneration. One or more glow plugs may be inserted in the trap housing, or a "Calrod" unit superimposed over the face of the particle trap structure. Still further, combustion aiding additives may be included in the fuel to promote burning off of the accumulated carbon. Where oxidation catalysts, e.g., palladium, and/or platinum, and/or rhodium are present within the catalytic converter/trap the temperatures encountered in regeneration are generally insufficient to adversely affect the catalyst system or the catalyst support.
The present invention provides a much less costly system readily adaptable to mass production for trapping particulates within a catalyst support member. Contrary to prior devices, the improved structures function in a manner different from prior devices in that the gas flows through the catalyst support from one side to the obverse side of the foil for at least a portion of its traverse through the system. Better entrapment of particulates, i.e., a better loading is secured before the pressure drop through the system becomes too great. At the same time, the normal catalytic conversion of internal engine combustion pollutants may be achieved.